Solar tracker system

ABSTRACT

A photovoltaic system includes a collection of photovoltaic modules, a base supporting the collection of photovoltaic modules, and a damper coupled between the collection of photovoltaic modules and the base. The damper resists movement of the photovoltaic modules relative to the base. The damper has a first damping ratio when the collection of photovoltaic modules moves at a first rate relative to the base and a second damping ratio when the collection of photovoltaic modules moves at a second rate relative to the base, and the damper passively transitions from the first damping ratio to the second damping ratio.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 17/287,607, filed Apr. 22, 2021, which is a National StageEntry of International PCT Application No. PCT/US2019/017818, filed Feb.13, 2019, which claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/629,931, filed Feb. 13, 2018. The aforementionedapplications are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present application is related to solar tracker systems for solarpanels.

BACKGROUND

Photovoltaic (PV) power systems frequently track the sun to variousdegrees to increase an amount of energy produced by the system. Thesetrackers typically move photovoltaic modules to adjust an angle ofincidence of the sunlight on the surface of the PV modules. Inparticular, trackers typically rotate the PV modules around an axisprincipally oriented north to south, tilting the modules to as much as60 degrees towards the east and west and adjusting tilt within thisrange throughout the day. By tracking the position of the sun, PV powersystems often produce 20-30% more energy than fixed-tilt systems.

A common configuration of horizontal single-axis trackers (“SAT”) asdescribed above includes a single actuator near the center of a row ofPV modules, potentially with 80-120 modules tilted by a single actuator.The angle of tilt is defined by the position of the actuator, while atorque tube or other similar device transfers moments and positions therest of the row at this tilt. However, environmental loading (wind,snow, dead load, etc.) can twist portions of a row away from theintended tilt angle. This effect requires design considerations that addcost in order to decrease risk of failures.

To reduce row twist, some PV systems may have shorter row lengths ormore than one actuator per row. These approaches can reduce the risk ofsystem failure from excessive row twist, but may increase the PV systemcost as well as overhead and maintenance costs. Furthermore, whenmultiple actuators are used, the actuators within a row must communicatesuch that, for example, other actuators stop moving if one actuatorfails. This communication can be by electronic, mechanical, or othermeans. However, this active control brings additional failure modes thatmust be considered in the design of the PV system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a photovoltaic system, according to one embodiment.

FIGS. 2A-2C illustrate an example damper.

FIG. 3 illustrates an example Durst curve.

The figures depict various embodiments of this disclosure for purposesof illustration only. One skilled in the art can readily recognize fromthe following discussion that alternative embodiments of the structuresand methods illustrated herein can be employed without departing fromthe principles of the invention described herein.

DETAILED DESCRIPTION

FIG. 1 illustrates a photovoltaic (PV) system 100, according to oneembodiment. As shown in FIG. 1 , the PV system 100 may include acollection of PV modules 110, an actuator 120, a controller 130, and adamper 140. The PV system 100 is configured to generate electricity, andmay be used alone or with other similar photovoltaic systems in, forexample, a photovoltaic power station.

The collection of PV modules 110 includes an array of one or morephotovoltaic modules configured to convert solar energy into electricityby the photovoltaic effect. The collection of PV modules 110 isrotatably anchored to a base 115, and may be coupled to a power grid,battery, or other power transmission or storage system. The amount ofelectricity produced by each photovoltaic module can be a function of atleast the angle of incidence of light on the surface of the module,where more energy is captured when light is perpendicular to the surface(i.e., a zero-degree angle of incidence) than when light is incident athigher angles.

The actuator 120 is configured to rotate the collection of PV modules110 around one or more axes. The actuator 120 may be a linear actuatorcoupled to the PV module collection 110 and a fixed position, such asthe base 115. Increasing or decreasing the length of the linear actuatorchanges a tilt angle of the collection of PV modules 110 with respect tothe base 115. Other types of actuators may be used in other embodiments.For example, the PV module collection 110 may be mounted on an axle anda rotary actuator may drive the axle to rotate the collection of PVmodules 110 around an axis. In one embodiment, the actuator 120 rotatesthe collection of PV modules 110 around an axis centered at the base 115and geographically oriented substantially north to south, such that asurface of the PV module 110 can be tilted between east- and west-facingangles. The actuator 120 may also rotate the collection of PV modules110 around additional axes (e.g., an east-west axis), or thephotovoltaic system 100 may include one or more additional actuators tocause other movements of the collection of PV modules 110.

The controller 130 drives the actuator 120 to set a tilt angle of thecollection of PV modules 110. To increase the amount of energy capturedby the collection of PV modules 110, the controller 130 may set the tiltangle based on a position of the sun. In one embodiment, the controller130 is coupled to a light sensor (not shown in FIG. 1 ) to detect aposition of the sun during the day. As the day progresses, thecontroller 130 may drive the actuator 120 to move the PV modulecollection 110 to follow the detected movement of the sun. Thus, thecontroller 130 drives the actuator 120 to move the PV module collection110 from an orientation facing substantially east to an orientationfacing substantially west. Overnight, the controller 130 may drive theactuator 120 to return the collection of PV modules 110 to aneast-facing orientation in preparation for sunrise the next morning, orthe controller 130 may drive the actuator 120 to rotate the PV modulecollection 110 in response to detecting sunlight in the east. Thecontroller 130 may alternatively control the tilt angle of the PV modulecollection 110 without light feedback, for example based on time of day.

The damper 140 provides damping for the PV system 100, resistingmovement of the PV modules 110 relative to the base 115. Damping by thedamper 140 can mitigate dynamic wind loading or other vibrational loadsapplied to the PV system 100. Wind loading can induce motion in PVsystem 100, for example rotating the collection of PV modules 110 aroundthe base at a velocity multiple orders of magnitude higher than themotion induced by the actuator 120. Although the damper 140 is shown inFIG. 1 as a component separate from the actuator 120 for purposes ofillustration, the damper 140 may be incorporated into or positionedconcentric to the actuator 120.

The damper 140 has a variable damping ratio. The damper 140 can have atleast a first damping ratio under a first operating condition and asecond damping ratio under a second operating condition. Differentdamping ratios may be advantageous for different operating states. Forexample, a high damping ratio enables the damper 140 to dissipate moreenergy, and therefore better mitigates undesired oscillations of the PVsystem 100 under wind loading than a low damping ratio. A high dampingratio also potentially enables the damper 140 to bear a portion of thestatic load of the PV module collection 110 and dynamic loads caused byenvironmental conditions, reducing the load on the actuator 120.However, a high damping ratio may cause the damper 140 to provide enoughresistance to the movement of the actuator 120 cause the PV module 110to twist away from its intended orientation. As a result of the modifiedangle of incidence caused by this “propeller effect,” the collection ofPV modules 110 may generate less electricity. If twisted more than a fewdegrees, operation of the collection of PV modules 110 may fall outsideacceptable specifications. A low damping ratio, in contrast, reduces thetwist by providing lower resistance to movement of the actuator 120.

Accordingly, the damper 140 can have a first damping ratio while the PVmodules 110 move at a first rate. The damper 140 can have a seconddamping ratio, higher than the first damping ratio, during a secondmovement rate of the PV modules 110 that is higher than the first rate.For example, the damping ratio can be relatively low when the PV modules110 move at low speeds relative to the base 115 (e.g., while theactuator 120 is moving the collection of PV modules 110 without highenvironmental loading) and relatively high when the PV modules 110 moveat higher speeds relative to the base (e.g., under dynamic windloading). The higher damping ratio of the damper 140 may enable thedamper 140 to support a portion of the loading on the PV system 100,including the static load of the PV module collection 110 (e.g., theweight of the collection 110) and static or dynamic loading caused byenvironmental conditions such as wind, snow, or dust. The lower dampingratio reduces the damper's resistance to movement caused by the actuator120. The damping ratio of the damper 140 can change passively based onthe operating state of the actuator 120, such as the actuation rate. Thedamping ratio may therefore be adjusted without active control by, forexample, the controller 130.

The higher damping ratio can have a value greater than 1 (such that thePV system 100 is overdamped), while not fully locking up the PV system100 under loading by wind or other environmental conditions. That is,the damper 140 under the higher damping ratio allows some movement ofthe system 100 while providing resistance against that movement.However, in some embodiments, the damper 140 may fully lock up underhigh environmental loading.

FIGS. 2A-2C show one example damper 140. FIG. 2A is a bottom cutawayview of the damper 140, while FIGS. 2B-2C are a side cutaway view of thedamper. The damper 140 can include a damper piston 210 that can movethrough fluid contained in a damper chamber 205. Any fluid or mixture offluids can be contained within the damper chamber 205, such as air,water, or oil. The damper piston 210 includes at least two ports 215that, when open, allow fluid to flow between the damper piston anddamper chamber. The ports 215 are shown in FIG. 2A as being openings ina bottom end of the damper piston, but the ports can be located anywherein the damper piston.

The two ports 215 can include at least one smaller diameter port 215Aand at least one larger diameter port 215B. The larger diameter port215A can be controlled by a valve 220. When the damper piston 210 movesthrough the fluid at low speeds (e.g., while the PV modules 110 arerotated at a low speed by the actuator 120), the fluid can flow freelythrough the large diameter port 215B and provide little resistance tothe movement of the piston. FIG. 2B illustrates an example of the piston210 moving at a low speed through the fluid. As shown in FIG. 2B, thevalve 220 is open and fluid can pass through the larger diameter port215B to flow into or out of the damper piston 210. At higher speeds, thevalve 220 is pushed closed and the fluid is forced through the smallerdiameter port 215A. The resistance provided by the fluid flow throughthe small diameter port 215A increases the effective damping ratio ofthe damper 140. FIG. 2C illustrates an example of the piston 210 movingat a high speed through the fluid. As shown in FIG. 2C, the valve 220 isclosed and fluid is forced through the smaller diameter port 215A toflow into or out of the damper piston 210.

The damper 140 may have configurations other than that shown in FIGS.2A-2C and may passively regulate the damping ratio in other manners. Forexample, valves may regulate fluid flow through multiple equally ordifferently sized ports in the damper piston. At lower speeds, thevalves are open to allow the fluid to flow through several or all of theports. At higher speeds, the valves close the port and force the fluidto flow through a smaller number of ports. As another example, thedamper 140 may include a non-Newtonian fluid that has lower viscosity atlow piston speeds and higher viscosity at high piston speeds.

The PV system 100 may be designed based on wind speed in the area wherethe system will be installed. In particular, the PV system 100 may bedesigned to withstand expected peak loads from the area's windconditions following a protocol such as ASCE 7. FIG. 3 illustrates anexample Durst curve, which relates average wind speed to gust duration,that may be used in such protocols. As shown in FIG. 3 , average windspeeds are higher for shorter measurements of gust duration than forlonger measurements. Because the damper 140 has a higher damping ratiounder wind loading and bears a portion of the load on the collection ofPV modules 110, the PV system 100 may be designed based on longer gustdurations—and therefore lower wind speeds—than photovoltaic systemslacking the damper 140. Furthermore, while the Durst curve shown in FIG.3 assumes free, unobstructed wind speed, the PV system 100 will likelyexperience turbulent air flow as dynamic winds move around thestructure. The average moments on the PV system 100 under turbulent flowmay be even lower across longer gust durations than predicted by theDurst curve. Accordingly, at least one of the base 115, the actuator120, and the PV modules 110 can be designed to withstand an averagevalue of moments applied to the PV system 100 across a specifiedduration of time. This duration of time can be calculated based on windtunnel testing, and can be, for example, approximately equivalent to aresponse time of the PV system 100 under target environmental loads. Thedesign for lower wind speeds may reduce the amount of material used toconstruct the base 115, the actuator 120, and the collection of PVmodules 110, and may reduce overhead and maintenance costs for the PVsystem 100.

In some embodiments, the higher damping ratio of the damper 140 isdesigned under wind tunnel testing to achieve a specified response timeof the PV system 100 under high environmental loads. Because the higherdamping ratio resists movement of the actuator 120, it may take longerfor the actuator 120 to move the PV modules 110 to a specified angleunder the higher damping ratio than under the lower damping ratio. Thehigher damping ratio can be selected such that the movement of the PVmodules 110 through a designated angular distance (relative to the base115) will take a specified amount of time if the PV system 100 issubjected to a specified amount of wind loading that is enoughenvironmental loading to cause the damper 140 to transition to thehigher damping ratio. For example, the higher damping ratio can beselected under wind tunnel testing such that the actuator moves the PVmodules 110 thirty degrees relative to the base in 60 seconds while thePV system 100 is subjected to a specified amount of wind loading above athreshold wind speed. The higher damping ratio can be selected to allowfaster or slower movements of the PV modules 110, such as 10 seconds, 30seconds, or 120 seconds.

Other Considerations

The foregoing description of various embodiments of the claimed subjectmatter has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit the claimedsubject matter to the precise forms disclosed. Many modifications andvariations can be apparent to one skilled in the art. Embodiments werechosen and described in order to best describe the principles of theinvention and its practical applications, thereby enabling othersskilled in the relevant art to understand the claimed subject matter,the various embodiments, and the various modifications that are suitedto the particular uses contemplated.

While embodiments have been described in the context of fullyfunctioning computers and computer systems, those skilled in the art canappreciate that the various embodiments are capable of being distributedas a program product in a variety of forms, and that the disclosureapplies equally regardless of the particular type of machine orcomputer-readable media used to actually effect the distribution.

Although the above Detailed Description describes certain embodimentsand the best mode contemplated, no matter how detailed the above appearsin text, the embodiments can be practiced in many ways. Details of thesystems and methods can vary considerably in their implementationdetails, while still being encompassed by the specification. As notedabove, particular terminology used when describing certain features oraspects of various embodiments should not be taken to imply that theterminology is being redefined herein to be restricted to any specificcharacteristics, features, or aspects of the invention with which thatterminology is associated. In general, the terms used in the followingclaims should not be construed to limit the invention to the specificembodiments disclosed in the specification, unless those terms areexplicitly defined herein. Accordingly, the actual scope of theinvention encompasses not only the disclosed embodiments, but also allequivalent ways of practicing or implementing the embodiments under theclaims.

The language used in the specification has been principally selected forreadability and instructional purposes, and it cannot have been selectedto delineate or circumscribe the inventive subject matter. It istherefore intended that the scope of the invention be limited not bythis Detailed Description, but rather by any claims that issue on anapplication based hereon. Accordingly, the disclosure of variousembodiments is intended to be illustrative, but not limiting, of thescope of the embodiments, which is set forth in the following claims.

1. (canceled)
 2. A system comprising: an actuator configured to positionat least one photovoltaic module; and a linear damper configured to dampforce applied to the at least one photovoltaic module, the linear damperincluding a variable damping ratio that varies passively as a functionof a current loading force on the at least one photovoltaic module,wherein the variable damping ratio is provided via a closed fluidicsystem, and wherein the at least one photovoltaic module experiencesloading forces in response to environmental stress and in response topositional adjustment via the actuator, and wherein the variable dampingratio of the linear damper is a first damping ratio in response to theenvironmental stress over a predetermined threshold and a second dampingratio in response to stress under the predetermined threshold includingthe positional adjustment via the actuator, the first damping ratiobeing higher than the second damping ratio and a transition between thefirst damping ratio and the second damping ratio is performed passively.3. The system of claim 2, wherein the at least one photovoltaic moduleis a first module in an array of photovoltaic modules that are eachdamped.
 4. The system of claim 2, wherein the variable damping ratioincreases in response to increases in the current loading force.
 5. Thesystem of claim 4, wherein the linear damper further comprises: a pistonconfigured to be driven by the current loading force on the at least onephotovoltaic module; and a piston chamber including a non-Newtonianfluid that increases in viscosity relative to the current loading forcedriving the piston.
 6. The system of claim 4, wherein the linear damperfurther comprises: a piston configured to be driven by the currentloading force on the at least one photovoltaic module and including avent that varies fluid flow area based on the current loading force; anda piston chamber including a fluid that resists motion of the piston,wherein the fluid is displaced in response to movement of the piston viathe vent having the varied fluid flow area.
 7. The system of claim 6,wherein the varied fluid flow area decreases in response to increases inthe current loading force.
 8. The system of claim 2, wherein a certaincurrent loading force causes a damping ratio that fully locks movementof the linear damper.
 9. The system of claim 2, wherein the actuator isconfigured to position the at least one photovoltaic module using a lowcurrent loading force with a corresponding low damping ratio.
 10. Thesystem of claim 2, wherein the linear damper further comprises: a firstport that enables fluid flow within the linear damper; and a second portthat enables fluid flow within the linear damper, wherein the secondport is passively closed while the linear damper operates at the firstdamping ratio.
 11. A solar tracker system, comprising: a mountconfigured to be affixed to a photovoltaic module and configured toenable the photovoltaic module to pivot about an axis; an actuatorconfigured to pivot an angular position of the photovoltaic module aboutthe axis and relative to the mount; and a linear damper configured to becoupled to the photovoltaic module and resisting angular positionadjustment of the photovoltaic module, wherein the linear damperexhibits a variable damping ratio as a function of a current loadingcondition of the photovoltaic module, wherein the variable damping ratiois provided via a closed fluidic system, and wherein the photovoltaicmodule experiences loading conditions in response to environmentalstress and in response to positional adjustment via the actuator, andwherein the variable damping ratio of the linear damper is a firstdamping ratio in response to the environmental stress over apredetermined threshold and a second damping ratio in response to stressunder the predetermined threshold including the positional adjustmentvia the actuator, the first damping ratio being higher than the seconddamping ratio and a transition between the first damping ratio and thesecond damping ratio is performed passively.
 12. The solar trackersystem of claim 11, wherein the variable damping ratio increases inresponse to increases in the current loading condition.
 13. The solartracker system of claim 12, wherein the linear damper further comprises:a piston configured to be driven by the current loading condition on thephotovoltaic module; and a piston chamber including a non-Newtonianfluid that increases in viscosity relative to the current loadingcondition driving the piston.
 14. The solar tracker system of claim 12,wherein the linear damper further comprises: a piston configured to bedriven by the current loading condition on the photovoltaic module andincluding a vent that varies fluid flow area based on the currentloading condition; and a piston chamber including a fluid that resistsmotion of the piston, wherein the fluid is displaced in response tomovement of the piston via the vent having the varied fluid flow area.15. The solar tracker system of claim 14, wherein the varied fluid flowarea decreases in response to increases in the current loadingcondition.
 16. The solar tracker system of claim 11, wherein a certaincurrent loading condition causes a damping ratio that fully locksmovement of the linear damper.
 17. The solar tracker system of claim 11,wherein the linear damper further comprises: a first port that enablesfluid flow within the linear damper; and a second port that enablesfluid flow within the linear damper, wherein the second port ispassively closed while the linear damper operates at the first dampingratio.
 18. A system comprising: an actuator configured to position atleast one photovoltaic module; and a linear damper configured to dampforce applied to the at least one photovoltaic module, the linear damperincluding a piston chamber with a piston therein, the piston configuredto be driven by a current loading force on the at least one photovoltaicmodule, the piston and the piston chamber providing a variable dampingratio that varies passively as a function of the current loading forceon the at least one photovoltaic module, wherein the at least onephotovoltaic module experiences loading forces in response toenvironmental stress and in response to positional adjustment via theactuator, and wherein the variable damping ratio of the linear damper isa first damping ratio in response to the environmental stress over apredetermined threshold and a second damping ratio in response to stressunder the predetermined threshold including the positional adjustmentvia the actuator, the first damping ratio being higher than the seconddamping ratio and a transition between the first damping ratio and thesecond damping ratio is performed passively.
 19. The system of claim 18,wherein the at least one photovoltaic module is a first module in anarray of photovoltaic modules that are each damped.
 20. The system ofclaim 18, wherein the variable damping ratio increases in response toincreases in the current loading force.
 21. The system of claim 19,wherein the piston chamber further includes a non-Newtonian fluid thatincreases in viscosity relative to the current loading force driving thepiston.
 22. The system of claim 19, wherein the piston further includesa vent that varies fluid flow area based on the current loading force,and wherein the piston chamber includes a working fluid that resistsmotion of the piston, wherein the working fluid is displaced in responseto movement of the piston via the vent having the varied fluid flowarea.
 23. The system of claim 22, wherein the varied fluid flow areadecreases in response to increases in the current loading force.
 24. Thesystem of claim 18, wherein a certain current loading force causes adamping ratio that fully locks movement of the linear damper.
 25. Thesystem of claim 18, wherein the actuator is configured to position theat least one photovoltaic module using a low current loading force witha corresponding low damping ratio.
 26. A system comprising: an actuatorconfigured to position at least one photovoltaic module; and a lineardamper physically separate from the actuator, the linear damperconfigured to damp force applied to the at least one photovoltaicmodule, the linear damper including a variable damping ratio that variespassively as a function of a current loading force on the at least onephotovoltaic module, wherein the at least one photovoltaic moduleexperiences loading forces in response to environmental stress and inresponse to positional adjustment via the actuator, and wherein thevariable damping ratio of the linear damper is a first damping ratio inresponse to the environmental stress and a second damping ratio inresponse to the positional adjustment via the actuator, the firstdamping ratio being higher than the second damping ratio and atransition between the first damping ratio and the second damping ratiois performed passively.
 27. The system of claim 26, wherein the at leastone photovoltaic module is a first module in an array of photovoltaicmodules that are each damped.
 28. The system of claim 26, wherein thevariable damping ratio increases in response to increases in the currentloading force.
 29. The system of claim 28, wherein the linear damperfurther comprises: a piston configured to be driven by the currentloading force on the at least one photovoltaic module; and a pistonchamber including a non-Newtonian fluid that increases in viscosityrelative to the current loading force driving the piston.
 30. The systemof claim 28, wherein the linear damper further comprises: a pistonconfigured to be driven by the current loading force on the at least onephotovoltaic module and including a vent that varies fluid flow areabased on the current loading force; and a piston chamber including afluid that resists motion of the piston, wherein the fluid is displacedin response to movement of the piston via the vent having the variedfluid flow area.
 31. The system of claim 30, wherein the varied fluidflow area decreases in response to increases in the current loadingforce.
 32. The system of claim 26, wherein a certain current loadingforce causes a damping ratio that fully locks movement of the lineardamper.
 33. The system of claim 26, wherein the actuator is configuredto position the at least one photovoltaic module using a low currentloading force with a corresponding low damping ratio.